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Kuechly, H. U., Kyba, C. C. M., Ruhtz, T., Lindemann, C., Wolter, C., Fischer, J., et al. (2012). Aerial survey and spatial analysis of sources of light pollution in Berlin, Germany. Remote Sensing of Environment, 126, 39–50.
Abstract: Aerial observations of light pollution can fill an important gap between ground based surveys and nighttime satellite data. Terrestrially bound surveys are labor intensive and are generally limited to a small spatial extent, and while existing satellite data cover the whole world, they are limited to coarse resolution. This paper describes the production of a high resolution (1 m) mosaic image of the city of Berlin, Germany at night. The dataset is spatially analyzed to identify the major sources of light pollution in the city based on urban land use data. An area-independent ‘brightness factor’ is introduced that allows direct comparison of the light emission from differently sized land use classes, and the percentage area with values above average brightness is calculated for each class. Using this methodology, lighting associated with streets has been found to be the dominant source of zenith directed light pollution (31.6%), although other land use classes have much higher average brightness. These results are compared with other urban light pollution quantification studies. The minimum resolution required for an analysis of this type is found to be near 10 m. Future applications of high resolution datasets such as this one could include: studies of the efficacy of light pollution mitigation measures, improved light pollution simulations, economic and energy use, the relationship between artificial light and ecological parameters (e.g. circadian rhythm, fitness, mate selection, species distributions, migration barriers and seasonal behavior), or the management of nightscapes. To encourage further scientific inquiry, the mosaic data is freely available at Pangaea: http://dx.doi.org/10.1594/PANGAEA.785492.
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Kyba, C. C. M., Ruhtz, T., Fischer, J., & Hölker, F. (2012). Red is the new black: how the colour of urban skyglow varies with cloud cover. Monthly Notices of the Royal Astronomical Society, 425(1), 701–708.
Abstract: The development of street lamps based on solid-state lighting technology is likely to introduce a major change in the colour of urban skyglow (one form of light pollution). We demonstrate the need for long-term monitoring of this trend by reviewing the influences it is likely to have on disparate fields. We describe a prototype detector which is able to monitor these changes, and could be produced at a cost low enough to allow extremely widespread use. Using the detector, we observed the differences in skyglow radiance in red, green and blue channels. We find that clouds increase the radiance of red light by a factor of 17.6, which is much larger than that for blue (7.1). We also find that the gradual decrease in sky radiance observed on clear nights in Berlin appears to be most pronounced at longer wavelengths.
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Kyba, C. C. M., Ruhtz, T., Fischer, J., & Hölker, F. (2011). Lunar skylight polarization signal polluted by urban lighting. J. Geophys. Res., 116(D24).
Abstract: On clear moonlit nights, a band of highly polarized light stretches across the sky at a 90 degree angle from the moon, and it was recently demonstrated that nocturnal organisms are able to navigate based on it. Urban skyglow is believed to be almost unpolarized, and is therefore expected to dilute this unique partially linearly polarized signal. We found that urban skyglow has a greater than expected degree of linear polarization (p = 8.6 ± 0.3%), and confirmed that its presence diminishes the natural lunar polarization signal. We also observed that the degree of linear polarization can be reduced as the moon rises, due to the misalignment between the polarization angles of the skyglow and scattered moonlight. Under near ideal observing conditions, we found that the lunar polarization signal was clearly visible (p = 29.2 ± 0.8%) at a site with minimal light pollution 28 km from Berlin's center, but was reduced (p = 11.3 ± 0.3%) within the city itself. Daytime measurements indicate that without skyglow pwould likely be in excess of 50%. These results indicate that nocturnal animal navigation systems based on perceiving polarized scattered moonlight likely fail to operate properly in highly light-polluted areas, and that future light pollution models must take polarization into account.
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Kyba, C. C. M., Ruhtz, T., Fischer, J., & Hölker, F. (2011). Cloud coverage acts as an amplifier for ecological light pollution in urban ecosystems. PLoS One, 6(3), e17307.
Abstract: The diurnal cycle of light and dark is one of the strongest environmental factors for life on Earth. Many species in both terrestrial and aquatic ecosystems use the level of ambient light to regulate their metabolism, growth, and behavior. The sky glow caused by artificial lighting from urban areas disrupts this natural cycle, and has been shown to impact the behavior of organisms, even many kilometers away from the light sources. It could be hypothesized that factors that increase the luminance of the sky amplify the degree of this “ecological light pollution”. We show that cloud coverage dramatically amplifies the sky luminance, by a factor of 10.1 for one location inside of Berlin and by a factor of 2.8 at 32 km from the city center. We also show that inside of the city overcast nights are brighter than clear rural moonlit nights, by a factor of 4.1. These results have important implications for choronobiological and chronoecological studies in urban areas, where this amplification effect has previously not been considered.
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Kyba, C. C. M., Ruhtz, T., Lindemann, C., Fischer, J., & Hölker, F. (2013). Two camera system for measurement of urban uplight angular distribution. AIP Conf. Proc, 1531(568).
Abstract: The angular distribution function of light emitted from cities is unknown, and represents the most important systematic error in skyglow simulations. We describe a method for measuring this distribution using a two camera system mounted on an aerial platform. We present preliminary results from a test flight using such a system, taken over the city of Berlin on July 14, 2011.
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Kyba, C. C. M., Tong, K. P., Bennie, J., Birriel, I., Birriel, J. J., Cool, A., et al. (2015). Worldwide variations in artificial skyglow. Sci. Rep., 5, 8409.
Abstract: Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope, and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ~5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program.
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Kyba, C. C. M., Wagner, J. M., Kuechly, H. U., Walker, C. E., Elvidge, C. D., Falchi, F., et al. (2013). Citizen science provides valuable data for monitoring global night sky luminance. Sci Rep, 3, 1835.
Abstract: The skyglow produced by artificial lights at night is one of the most dramatic anthropogenic modifications of Earth's biosphere. The GLOBE at Night citizen science project allows individual observers to quantify skyglow using star maps showing different levels of light pollution. We show that aggregated GLOBE at Night data depend strongly on artificial skyglow, and could be used to track lighting changes worldwide. Naked eye time series can be expected to be very stable, due to the slow pace of human eye evolution. The standard deviation of an individual GLOBE at Night observation is found to be 1.2 stellar magnitudes. Zenith skyglow estimates from the “First World Atlas of Artificial Night Sky Brightness” are tested using a subset of the GLOBE at Night data. Although we find the World Atlas overestimates sky brightness in the very center of large cities, its predictions for Milky Way visibility are accurate.
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Schnitt, S., Ruhtz, T., Fischer, J., Hölker, F., & Kyba, C. C. M. (2013). Temperature stability of the sky quality meter. Sensors (Basel), 13(9), 12166–12174.
Abstract: The stability of radiance measurements taken by the Sky Quality Meter (SQM)was tested under rapidly changing temperature conditions during exposure to a stable light field in the laboratory. The reported radiance was found to be negatively correlated with temperature, but remained within 7% of the initial reported radiance over a temperature range of -15 degrees C to 35 degrees C, and during temperature changes of -33 degrees C/h and +70 degrees C/h.This is smaller than the manufacturer's quoted unit-to-unit systematic uncertainty of 10%,indicating that the temperature compensation of the SQM is adequate under expected outdoor operating conditions.
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